STS 304 and STS 316L are the most commonly used stainless steel for shipyards and offshore plants of which a surface layer is contaminated or deformed due to scratch by external exposure and oxidation by welding, thereby causing rusts and corrosions.
Normal stainless steel includes Fe as a basic component, Cr and Ni as main components, and Mo, Ti, Mn, Zr, Nb, N or the like in a small amount.
Currently, the stainless steel is shipped to plates, coils, steel pipes and other products through schemes such as cold rolling, welding, heat treatment, pickling and passive film treatment.
In addition, FeO, Fe3O4, Fe2O3, NiiO, Ni3O4, Ni2O3, CrO3 and Cr2O3 are mainly formed on the oxidized surface.
Accordingly, when the oxidized surface has many Cr2O3 and NI203, acid resistance, corrosion resistance and oxidation resistance become strong, so that rusts are not easily generated.
In addition, regarding iron oxide, the acid resistance, corrosion resistance and oxidation resistance are strong in an order of Fe2O3, Fe3O4, and FeO.
In addition, in the case of conventional pickling and passivating agents, most are processed with an acid atmosphere or an acid solution and hazardous chemical substances are contained therein.
As for some neutral solutions, acid and basic chemical substances used as raw materials are also classified as hazardous chemical substances, therefore the hazardous chemical substances should be indicated in substance information for products formed of those substances.
Currently, when the hazardous chemical substances are used, chemical safety protective equipment should be worn during work, and preventive facilities should be provided based on Chemical Control Act and Occupational Safety and Health Act.
Particularly in the shipbuilding and plant industries, a zone for pickling and passivating work should be controlled and the work should be prohibited from being performed in parallel with another work.
In addition, when ships and offshore plants are constructed, because stainless steel pipes and structures are installed on the ship or in the field, and the installed pipes and structures are contaminated or corroded by welding, the pickling and passive film treatment is required.
In general, the treatment is processed using a strong acid solution obtained by mixing nitric acid, sulfuric acid, hydrochloric acid and hydrofluoric acid as pickling and passivating agents. At this time, when the acid solution agent flows down to a floor surface or when a washing solution flows down to the floor during washing work, the acid solution agent generally is reacted with coated epoxy resin, thereby causing discoloration or deformation, thus sometimes the floor is required to be coated again.
In addition, because of the strong acid agent, the agents need to be neutralized with a basic agent and finally washed with clear water, and because of using hazardous chemical substances, a workplace should be controlled, another work cannot be performed concurrently, and chemical safety protection equipment and preventive substances should also be provided.
An object of the present disclosure is to shorten a process in which the neutral agent of 6.9 pH to 7.1 pH is used as a pickling and passivating agent, so that water washing is implemented without neutralization using a basic agent during the process.
In addition, the neutral agent which does not react with the resin prevents a coating portion from being discolored and deformed, so that convenience in use is improved.
In addition, since raw materials of the product have no hazardous chemical substances, the raw materials are not regulated by Chemical Control Act, Safety Control of Dangerous Substances Act, and Occupational Safety and Health Act, so that it is convenient for works.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.